![]() Therefore, through the Middle Ages, alchemists and other writers do not seem to have discriminated the two salts accurately from each other. : 766–767 Alum described in medieval texts Īlum and green vitriol (iron sulfate) both have sweetish and astringent taste, and they had overlapping uses. The alumen of the ancients, then, was not always potassium alum, not even an alkali aluminum sulfate. Pliny describes several other types of alumen but it is not clear as to what these minerals are. In some places the iron sulfate may have been lacking, so the salt would be white and would be suitable, according to Pliny, for dyeing bright colors. Contamination with iron sulfate was greatly disliked as this darkened and dulled dye colours. This property seems to characterize a solution of iron II sulfate in water a solution of ordinary (potassium) alum would possess no such property. One kind of alumen was a liquid, which was apt to be adulterated but when pure it had the property of blackening when added to pomegranate juice. From the name schiston and the mode of formation, it appears that this kind was the salt that forms spontaneously on certain salty minerals, as alum slate and bituminous shale, and consists chiefly of sulfates of iron and aluminium. Pliny wrote that there is another kind of alum that the Greeks call schiston, and which "splits into filaments of a whitish colour". Pliny wrote that different substances were distinguished by the name of alumen, but they were all characterised by a certain degree of astringency, and were all employed in dyeing and medicine. Pliny informs us that a form of alumen was found naturally in the earth, and calls it salsugoterrae. īy comparing Pliny's description with the account of stupteria given by Dioscorides, it is obvious the two are identical. Alumen in Pliny and Dioscorides Ī detailed description of a substance called alumen occurs in the Roman Pliny the Elder's Natural History. Native alumen from the island of Melos appears to have been a mixture mainly of alunogen ( AlĢO) with potassium alum and other minor sulfates. The site was abandoned in the 7th century CE, but dates back at least to the 2nd century CE. ![]() ![]() The production of potassium alum from alunite is archaeologically attested on the island Lesbos. The Ancient Greek Herodotus mentions Egyptian alum as a valuable commodity in The Histories. The western desert of Egypt was a major source of alum substitutes in antiquity. History Alum found at archaeological sites In medicine, "alum" may also refer to aluminium hydroxide gel used as a vaccine adjuvant. In most industries, the name "alum" (or "papermaker's alum") is used to refer to aluminium sulfate, AlĢO, which is used for most industrial flocculation : 766 (the variable n is an integer, whose size depends on the amount of water absorbed into the alum). The most common of these analogs is chrome alum KCr(SO The name "alum" is also used, more generally, for salts with the same formula and structure, except that aluminium is replaced by another trivalent metal ion like chromium III, and/or sulfur is replaced by another chalcogen like selenium. Other alums are named after the monovalent ion, such as sodium alum and ammonium alum. By itself, "alum" often refers to potassium alum, with the formula KAl(SOĢO. An alum ( / ˈ æ l ə m/) is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula XAl(SOĢO, where X is a monovalent cation such as potassium or ammonium.
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